1. Field of the Invention
The present invention relates to an endoscope and, more particularly, to the constitution of an apparatus for use in a medical field for forming and displaying a spectral image (or video image), which is represented by image information obtained in an optionally selected wavelength range.
2. Description of the Related Art
In recent years, among electronic endoscope apparatuses employing solid-state image pickup devices, an electronic endoscope adapted to perform spectroscopic imaging by combining narrow band bandpass filters according to spectral reflectance obtained at a digestive organ, such as gastric mucosa, that is, an electronic endoscope apparatus with a built-in narrow band bandpass filter (or NBI (narrow band imaging) filter) has received attention. This apparatus is provided with three narrow (wavelength) band bandpass filters, instead of frame sequential type RGB rotary filters. The apparatus sequentially outputs illuminating light rays through these narrow band bandpass filters. Then, the apparatus performs processing similar to that performed on R, G, and B (RGB) signals by simultaneously changing weights assigned to three signals obtained by these illuminating light rays. Consequently, the apparatus forms a spectral image. According to such a spectral image, a microstructure, which could not be obtained in a digestive organ such as a large or small bowel by a related apparatus, is extracted.
Meanwhile, it has been proposed to form a spectral image by performing computation according to an image signal, which is obtained by white light, in an endoscope apparatus of the synchronous system type configured to dispose minute mosaic color miters at a solid-state image pickup device as disclosed in JP-A-2003-93336 and Yoichi Miyake: Analysis and Evaluation of Digital Color Images, University of Tokyo Press, pp. 148 to 153 (2000), instead of the above endoscope apparatus of the frame sequential type using the narrow band bandpass filters. The proposed apparatus first obtains matrix data (representing a coefficient set) representing the relation between numerical data, into which an RGB color sensitivity characteristic is converted, and numerical data, into which a spectral characteristic of a specific narrow band bandpass filter is converted. Then, the proposed apparatus obtains spectral-image signals representing an estimated spectral image through narrow band bandpass filters by performing computation on the matrix data and RGB-signals. In the case of forming a spectral image by such computation, there is no need for preparing a plurality of filters respectively corresponding to a desired wavelength range. Also, the proposed apparatus eliminates the replacement of such filters. Thus, the size of the apparatus is prevented from being made to be large. Consequently, the cost of the apparatus can be reduced.
Incidentally, a wavelength range optimal in forming and displaying a clinically easily observable spectral image often varies with operators, such as a clinical doctor, of the apparatus. Thus, even in a case where a wavelength range considered to be optimal for a part of an object to be observed is preliminarily set in the apparatus, a clinical doctor may be unable to utilize the set wavelength range at the formation of a spectral image and to help selecting a wavelength range conforming to his feeling.
In such a case, the operator gradually changes the preliminarily set wavelength range. To perform such a changing operation, it is preferable to provide a wavelength memory section or region for storing, after a wavelength range is changed, an obtained wavelength range therein, which is utilized to form a spectral image. Such a memory section or region can be distinguished from other storage section or regions which respectively store the preliminarily set wavelength range and the optimal wavelength range corresponding to each clinical doctor. Thus, such a memory section or region can prevent an occurrence of a trouble that the wavelength range obtained in the changing operation is erroneously overwritten on the wavelength range stored in one of the other storage section or regions and is erroneously stored therein.
However, in the case where the wavelength memory section or region adapted to store, after the wavelength range is changed, the wavelength range obtained to be utilized to form a spectral image is provided separately from the other storage section or regions, usually, many operators of the apparatus frequently updates the wavelength range stored and saved in the wavelength memory section or region. Thus, in a case where a new wavelength range is set by utilizing the wavelength range stored and saved therein as a reference, the reference is frequently changed. Consequently, it is extremely likely to cause a trouble in the setting of a new wavelength range.
To prevent an occurrence of such a drawback, for example, it has been considered to automatically reset data representing the wavelength range stored in the wavelength memory section or region to an initially set value at each turnoff of a power supply due to termination of use of an endoscope apparatus. However, in this case, it is necessary to turn off the power supply each time when an operator resets the data representing the wavelength range stored in the wavelength memory section or region to the initially set value during the use of the endoscope apparatus. Consequently, the efficiency in forming and displaying a spectral image is extremely reduced.